In the three other cases, from half a dozen to a dozen
tentacles, both laterally and towards the centre, were well inflected
or sub-inflected. Lastly, in [page 236] ten other experiments, minute
bits of meat were placed on a single gland or on two glands in the
centre of the disc. In order that no other glands should touch the
meat, through the inflection of the closely adjoining short tentacles,
about half a dozen glands had been previously removed round the
selected ones. On eight of these leaves from sixteen to twenty-five of
the short surrounding tentacles were inflected in the course of one or
two days; so that the motor impulse radiating from one or two of the
discal glands is able to produce this much effect. The tentacles which
had been removed are included in the above numbers; for, from standing
so close, they would certainly have been affected. On the two remaining
leaves, almost all the short tentacles on the disc were inflected. With
a more powerful stimulus than meat, namely a little phosphate of lime
moistened with saliva, I have seen the inflection spread still farther
from a single gland thus treated; but even in this case the three or
four outer rows of tentacles were not affected. From these experiments
it appears that the impulse from a single gland on the disc acts on a
greater number of tentacles than that from a gland of one of the
exterior elongated tentacles; and this probably follows, at least in
part, from the impulse having to travel a very short distance down the
pedicels of the central tentacles, so that it is able to spread to a
considerable distance all round.
Whilst examining these leaves, I was struck with the fact that in six,
perhaps seven, of them the tentacles were much more inflected at the
distal and proximal ends of the leaf (i.e. towards the apex and base)
than on either side; and yet the tentacles on the sides stood as near
to the gland where the bit of meat lay as did those at the two ends. It
thus appeared as [page 237] if the motor impulse was transmitted from
the centre across the disc more readily in a longitudinal than in a
transverse direction; and as this appeared a new and interesting fact
in the physiology of plants, thirty-five fresh experiments were made to
test its truth. Minute bits of meat were placed on a single gland or on
a few glands, on the right or left side of the discs of eighteen
leaves; other bits of the same size being placed on the distal or
proximal ends of seventeen other leaves. Now if the motor impulse were
transmitted with equal force or at an equal rate through the blade in
all directions, a bit of meat placed at one side or at one end of the
disc ought to affect equally all the tentacles situated at an equal
distance from it; but this certainly is not the case. Before giving the
general results, it may be well to describe three or four rather
unusual cases.
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